Editorial: eliminate accidental ambiguity in Punctuator

PR tc39#1646 introduced an ambiguity to the lexical grammar:
Punctuator derives OtherPunctuator in two different ways --
directly, and indirectly via OptionalChainingPunctuator.

It doesn't make sense for OptionalChainingPunctuator to derive OtherPunctuator,
so I've eliminated that alternative.

spec.html

@@ -11100,7 +11100,6 @@ <h2>Syntax</h2>
     <emu-grammar type="definition">
       OptionalChainingPunctuator ::
         `?.` [lookahead &lt;! DecimalDigit]
-        OtherPunctuator
 
       OtherPunctuator :: one of
         `{` `(` `)` `[` `]`